Fix constraint instantiator to load correct constraint (#208)

Loading constraint that are defined in the Model first and afterwards from reference.

Author: michelu89

core/libs/instantiator/src/lib/instantiators/constraint-instantiator.ts

@@ -30,10 +30,9 @@ export class ConstraintInstantiator extends BaseConstraintCharacteristicInstanti
   }
 
   create(quad: Quad): Constraint {
-    const extReference = this.namespaceCacheService.findElementOnExtReference<Characteristic>(quad.object.value);
-    if (extReference) {
-      extReference.setExternalReference(true);
-      return extReference;
+    let constraint = this.cachedFile.getElement<Constraint>(quad.object.value);
+    if (constraint) {
+      return constraint;
     }
 
     if (!this.rdfModel.store.getQuads(quad.object, null, null, null).length) {
@@ -44,7 +43,7 @@ export class ConstraintInstantiator extends BaseConstraintCharacteristicInstanti
       return externalReference;
     }
 
-    const constraint = super.create(quad);
+    constraint = super.create(quad);
     constraint.setExternalReference(this.rdfModel.isExternalRef);
     constraint.fileName = this.metaModelElementInstantiator.fileName;